1. Field of the Invention
The present invention relates to a charging control apparatus for a vehicle in which the rate of increase in a current flowing through a field winding is controlled to increase a generator voltage gradually, and more particularly, to a charging control apparatus which prevents malfunction of a charging abnormality warning device.
2. Description of the Related Art
A charging control apparatus is disclosed in JP-A-59-83600 (corresponding to U.S. Pat. No. 4,459,489). In the disclosed charging control apparatus, when a large electric load is applied, it is detected that an output voltage of a generator drops down to a predetermined value (0.5 V) and below, and, in response to the result of detection, the conduction rate is increased gradually from the conduction rate of switching means before an electric load is applied, which switching means is connected in series with a field winding.
By gradually increasing the current flowing through the field winding, the load on the generator is gradually applied to an engine to which the generator is coupled, so that the engine can be prevented from vibration or stalling.
Further, in the charging abnormality detection display described in JP-A-49-38167, when electric generation is controlled so that a battery voltage assumes a first predetermined value V.sub.R1, charging abnormality is detected and a charging abnormality warning lamp is turned on when the generator output voltage drops to assume a second predetermined value V.sub.R2 and below which has been set to be smaller than the first predetermined value V.sub.R1. However, such a state may be caused by intermittent application of a load, etc., even if the apparatus is normally operative. Therefore, the charging abnormality warning lamp is prevented from being turned on, even if the generator output voltage drops to assume the second predetermined value V.sub.R2 and below, so far as the battery voltage has the first predetermined value V.sub.R1 and above. Further, even when the battery voltage drops to assume the first predetermined value VR.sub.1 and below and the generator starts electric generation in a state where the output voltage of the generator has dropped to assume the second predetermined value V.sub.R2 and below at the time of intermittent application of a load, it takes time for the generator output voltage to reach the second predetermined value V.sub.R2. Therefore, taking a build-up time of the generator into consideration, mislighting or erroneous lighting of the charging abnormality warning lamp is prevented by having a charging abnormality detection signal delayed for a predetermined time (delay time).
In the charging control apparatus described above, however, it happens sometimes that the charging abnormality warning lamp is turned on erroneously notwithstanding that a delay time has been set in the charging abnormality detection device.
More precisely, when a large electric load is cut off in a state where the generator is in operation under the application of the large electric load, the battery voltage rises for a moment due to charging of the battery by the generator. Thereafter, since it is necessary for the battery to supply a current only to a small load connected to this battery, the battery voltage falls very slowly as shown in FIG. 3 (a). At this time, however, the battery voltage has a value higher than the first predetermined value V.sub.R1. Accordingly, the voltage of a stator winding which is the generator voltage, drops to assume the second predetermined value V.sub.R2 and below as shown in FIG. 3 (g). Thereafter, just when the battery voltage drops to assume the first predetermined value V.sub.R1 and below, the conduction rate of the switching means begins to increase gradually, and the current flowing through the field winding is increased gradually. Here, since the switching means has continued to stay in an OFF state, the conduction rate of the switching means increases gradually from 0%. Thus, as shown by a broken line in FIG. 3 (g), it takes a very long time for the voltage of the stator winding to reach the second predetermined value V.sub.R2 and above.
Thus, the generator voltage cannot be recovered to the second predetermined value V.sub.R2 within a predetermined delay time, and hence the charging abnormality warning lamp is turned on erroneously notwithstanding that the generator is operating normally.